The present invention relates to a torque transmitting belt, and ore particularly to a torque transmitting endless belt spanned between input and output pulleys which include each circumferential groove of a V-shaped cross-section to transmit a torque between the pulleys.
There has been known a continuously variable transmission (CVT) comprising a torque transmitting belt extending between an input (driving) pulley and an output (driven) pulley, the ratio capable of being varied (ratio being defined as the RPM or speed ratio between the input and output pulleys), by adjusting the size of a V-shaped groove(s) in one or both of the pulleys as a result of the variation of the pressure which forces the belt into groove(s). Thus, the position of the belt on the pulleys and the effective diameter of the pulleys can be varied, which makes it possible to continuously vary the ratio between the input and output pulleys.
In the above-described CVT, such a torque transmitting belt has been employed as the belt comprises an endless carrier spanned between the pulleys and a plurality of torque transmitting blocks which are mounted by the endless carrier so that the blocks may be longitudinally shiftable along the endless carrier and which engage with the circumferential grooves of the pulleys at both end surfaces thereof and further engage with the endless carrier.
In this endless belt, the blocks are transmitted with a torque at the input (driving) pulley. The torque transmitting blocks gradually shift with the endless carrier toward the output (driven) pulley while the blocks contact with adjacent blocks each other. The blocks transmit the torque from the input pulley to the output pulley. Thus, the transmission of a torque is made from the input pulley and the output pulley.
In general, torque transmitting blocks are mounted on an endless carrier under the condition that the endless carrier extends through grooves provided on the torque transmitting blocks. There is known a torque transmitting block having a groove which opens at the position adjacent an inner surface of a pulley and which is closed by a member of the torque transmitting block. One of the above-described examples is disclosed in Japanese Laying-open Patent Publication No. Sho 57-23820. The torque transmitting block has a surface within the groove of the troque transmitting block, which an endless carrier contacts to transmit the torque between the endless carrier and the block.
An endless carrier comprises a plurality of belt-shaped hoops which are superimposed thereon. For example, an endless carrier comprises ten to fourteen hoops which are superimposed thereon. In general, a hoop is made of metal. Recently, a hoop made of plastics is also proposed.
Heretofore, the surface of a torque transmitting block which an endless carrier contact is formed to be upwardly rounded. When an endless carrier contacts the rounded surface of a torque transmitting block to transmit a torque therebetween, the endless carrier moves toward the highest position among the rounded surface of the block by the centering operation. This centering of the endless carrier prevents the endless carrier from moving in the lateral direction of the belt. Hence, in general, end surfaces of hoops which form the endless carrier are prevented from being struck on an inner surface of a pulley and a member of the block, which closes the groove at its inner end.
On the other hand, when the control pressure supplied into a hydraulic actuator of a pulley is low, the above-described centering operation is not sufficiently made. As shown in FIG. 8, hoops 11a, 11b, . . . , 11n move in the lateral direction of the block.
When the control pressure supplied into a hydraulic actuator of a pulley is low, both magnitude of the vertical force exerted between a contact surface 13a of an endless carrier and a contact surface of an innermost hoop 11a and the magnitude of the vertical force exerted between the contact surfaces among the hoops 11a, 11b, . . . , 11n, are small. Hence, the hoops 11a, 11b, . . . , 11n may move on a rounded contact surface 13a toward one end of the block in the lateral direction of the block. When the hoops 11a, 11b, . . . , 11n move in the direction toward a neck portion 12b of a block 12 and strike on the neck portion 12b, the discontinuous surface of the neck portion 12b contacts the end surfaces of the hoops 11a, 11b, . . . , 11n and slides on them. This contact happens to generate cracks and scratches on the end surfaces of the hoops 11a, 11b, . . . , 11n. As a result, this causes a stress concentration, thereby shortening the life of the hoops.
On the other hand, when the hoops 11a, 11b, . . . , 11n move in the direction toward the opening of the groove 13 to contact the surface 2 of the pulley and slide on the surface 2, the surface 2 of the pulley is a continuous surface, and the contact beween the hoops and the surface 2 of the pulley does not generate cracks nor scratches on the end surfaces of the hoops 11a, 11b, . . . , 11n. Hence, when the hoops 11a, 11b, . . . , 11n moves in the direction toward the opening of the groove 13 to contact the surface 2 of the pulley, the end surfaces of the hoops 11a, 11b, . . . , 11n are almost not damaged.
The movement of the hoops 11a, 11b, . . . , 11n in the lateral direction of blocks may happen to be made at the time other than the time when the control pressure supplied into a hydraulic actuator is low. That is, the hoops 11a, 11b, . . . , 11n slide each other by the difference of the circumferential speed between hoops. When the coefficient of friction generated among hoops 11a, 11b, . . . , 11n decreases to lower the frictional force, the hoops 11a, 11b, . . . , 11n may move in the lateral direction of the block.